During the processing of a semiconductor wafer to its ultimate finished product as an integrated circuit device or chip, there are many photolithographic steps used to develop patterns in the wafer. As the size of the wafer topography becomes smaller and smaller, wherein the linewidths are on the order of several micrometers, if not in submicrometer dimensions, the photolithography processing steps become significantly important to provide very precise alignment, positioning and focusing of the wafer relative to the mask within the photolithography equipment.
Conventional apparatus for supporting wafers provided with photoresist material during the photolithography steps are known to generate debris of photoresist material from the wafer surface during the loading and unloading steps of the wafer onto and from a wafer support plate of the apparatus. In particular, in one form of apparatus finger-like supports or tabs are provided to be pressed against the photoresist surface of the wafer to hold it in position within a generally circular cut-out of the wafer support plate through which a mask image is projected. The support tabs can and often do cause photoresist debris (1) by impact when the wafer holding chuck assembly of the apparatus pushes the wafer against the tabs, and (2) by a rubbing movement between the wafer surface and the support tabs when the wafer is withdrawn from the support plate. Accumulated debris collected on the tab surface can result in an image generated by the mask on the wafer to be out of focus by alteration of the focal plane on portions if not the entire wafer surface. This results in poor image definition and loss of control of critical spacing and linewidth dimensions, particularly dimensions in the micron and submicron range. Moreover, the loss of dimension control results in low yield of product wafers which either must be discarded or reworked.
It is important in this field to provide a wafer support plate that reduces, if not eliminates, the generation of photoresist material debris from wafers during the photolithographic alignment and focusing steps.